Sophorolipids (SLs) belong to the family of microbial glycolipids whose chemical structure imparts natural surfactancy. They are typically produced from renewable substrates by fermentation and provide the added benefits of biocompatibility and biodegradability (Develter, D. W. G., and L. M. L. Lauryssen, Eur. J. Lipid Sci. Technol., 112: 628-638 (2010)). Sophorolipids are typically made up of a disaccharide (sophorose; 2-O-β-D-glucopyranosyl-β-D glucopyranose) attached to a hydroxy fatty acid through a glycosidic linkage (FIG. 1). The specific location of those chemical bonds is dependent on the microbial strain used to produce the SLs. The most well-known SLs are naturally synthesized in high yields by the yeast Candida bombicola (Ashby, R. D., et al., Biotechnol. Lett., 30: 1093-1100 (2008)), and the glycosidic bond generally occurs between the 1′ hydroxy group of the sophorose sugar and the ω or ω-1 carbon of the fatty acid. In these SLs, the 6′ and 6″ hydroxy groups of the sophorose are sites of potential acetylation and the fatty acid chain length varies between 16 (C-16) and 18 (C-18) carbons and may be saturated or unsaturated. Studies have shown that the preferred structural conformation of SLs produced by C. bombicola from glucose and palmitic acid (SL-p), oleic acid (SL-o) or stearic acid (SL-s) is as a lactone where the carboxylic acid group of the fatty acid is esterified to the disaccharide ring at carbon 4″ (Nuñez, A., et al., Chromatographia, 53: 673-677 (2001)). Other strains of Candida such as C. apicola (Hommel, R. K., and K. Huse, Biotechnol. Lett., 33: 853-858 (1993)) and C. batiste (Konishi, M., et al., J. Oleo. Sci., 57: 359-369 (2008)) have been documented to synthesize SLs, and recently 3 new strains of Candida (C. riodocensis, C. stellata and Candida sp. Y-27208) were discovered to produce SLs with very little lactone form (Kurtzman, C. P., et al., FEMS Microbiol. Lett., 311: 140-146 (2010)). Another less well-known SL producer is the yeast Rhodotorula bogoriensis which generally produces SLs containing 13-hydroxydocosanoic acid (C-22) as the fatty acid moiety which is entirely in the free acid conformation (Nuñez, A., et al., Biotechnol. Lett., 26: 1087-1093 (2004); Cutler, A. J., and R. J. Light, J. Biol. Chem., 254: 1944-1950 (1979); Cutler, A. J., and R. J. Light, Can. J. Microbiol., 28: 223-230 (1982)).
Large production capacity from C. bombicola (reportedly as high as 422 g/L when using whey and rapeseed oil as substrates (Daniel, H.-J., et al., Biotechnol. Lett., 20: 1153-1156 (1998)) have increased awareness of SL applications (Solaiman, D. K. Y., et al., Inform, 15: 270-272 (2004)). Acetylated lactones have proven effective as additives in shampoos, body washes, and detergents (Hall, P., et al., U.S. Pat. No. 5,417,879; Inoue, S., et al., U.S. Pat. No. 4,215,213), and as emulsifiers for skin care products (Mager, H., et al., European Patent EP 0209783) and structured lipid emulsions (Xue, C.-L., et al., J. Am. Oil Chem. Soc., 90: 123-132 (2013)). In addition, they have been reported to have applications as food encapsulants (Allingham, R., U.S. Pat. No. 3,622,344), as degreasing agents (Hall et al. 1995), and to enhance soil bioremediation and waste water treatment (Makkar, R., and R. Cameotra, Appl. Microbiol. Biotechnol., 58: 428-434 (2002); Mulligan, C., et al., J. Hazard. Mater., 85: 111-125 (2001). Studies have also shown that the lactone form of sophorolipids has antimicrobial properties (Ashby, R. D., et al., New Biotechnol., 28: 24-30 (2011); Solaiman, D. K. Y., et al., Biocatal. Agric. Biotechnol., 4: 342-348 (2015)) and can be utilized as a bacteriostatic agent (Mager et al. 1987), as spermicides and virucides (Shah, V., et al., Antimicrob. Agents Chemother., 49: 4093-4100 (2005)), as septic shock antagonists (Bluth, M. H., et al., Crit. Care Med., 34: 188-195 (2006); Hardin, R., et al., J. Surg. Res., 142: 314-319 (2007)), as anticancer agents (Chen, J., et al., Enz. Microb. Technol., 39: 501-506 (2006); Fu, S. L., et al., J. Surg. Res., 148: 77-82 (2008)), as stimulant for skin fibroblast metabolism (Borzeix, C., U.S. Pat. No. 6,596,265), and as treatment for skin diseases (Maingault, M., Canadian Patent CAN126242874). In contrast, the acidic form of SLs has been shown to be therapeutically active for skin treatment, particularly as agents for fibrinolysis (promoting healing), desquamation, depigmenting, macrophage activation (Maingault, M., U.S. Pat. No. 5,981,497), and as moisturizing agents (Abe, Y., et al., U.S. Pat. No. 4,297,340; Tsutsumi, H. et al., U.S. Pat. No. 4,305,961). These characteristics have aided in the progress of the industrial utilization of SLs such that they are currently being successfully developed and used in dishwashing detergents by Saraya Co., Ltd. under the trade name Sophoron™, and by Ecover and Soliance for applications in laundry and dishwashing detergents, industrial and institutional cleaners, hand soaps, and cosmeceuticals. In addition, the unique sophorolipid (SL) structure has increased interest in their use as a precursor for the production of specialty chemicals such as sophorose, a known inducer of fungal cellulase enzymes (Sternberg, D., and G. Mandels, J. Bacteriol., 144: 1197-1199 (1980)), monohydroxy fatty acids (Rau, U., et al., Ind. Crop Prod., 13: 85-92 (2001)), and other derivatives (Zerkowski, J., and D. Solaiman, J. Am. Oil Chem. Soc., 83: 621-628 (2006); Zerkowski, J., and D. Solaiman, J. Am. Oil Chem. Soc., 84: 463-471 (2007); Zerkowski, J., et al., J. Am. Oil Chem. Soc., 85: 277-284 (2008)). To a limited extent, structural variation (and hence control over physical properties) can be achieved by changing the hydrophobic carbon source which alters the sophorolipid fatty acid content.
Sugars and sweeteners have an important role in the human diet, and their uses are often determined by their economics and availability, and their suitability in a particular food. Non-caloric sweeteners have been used by consumers for more than 30 years. Although it helped the consumers' need for non-caloric artificial sweeteners, many consumers express interest in additional products, especially products containing natural non-caloric sweeteners. Consumer interest in natural high-potency sweeteners has grown dramatically in recent years, fueled by concerns about the use of artificial additives in foods.
Taste is a sensory response to chemical stimulation of taste receptors by tastants. There are five basic tastes that have been identified: salty, sweet, sour, bitter, and umami. Taste receptor cells are responsible for transducing chemical stimuli from the mouth and relaying information to the nervous system. Sweet stimuli utilize G-protein coupled receptors which activate the phospholipase C (PLC) signaling pathway. The T1R3 receptor subunit acts as a sweet taste receptor in combination with its partner, T1R2. Sweet receptors are activated by a vast repertoire of chemically distinct molecules which specifically interact with certain regions of T1R2+T1R3 sweet receptors (Bachmanov, A. A., and G. K. Beauchamp, Annu. Rev. Nutr., 27: 389-414 (2007); Bachmanov, A. A., et al., Curr. Pharm. Design., 20(16): 2669-83 (2014)).
Sweet is the main attractive taste modality in humans. However, increasing amounts of sugars in food have raised concern about their health effects. The steady increase of the daily consumption of dietary sugar over the last few decades may have contributed to the obesity epidemic and the early onset of type-II diabetes observed in many countries (Malik, V. S., et al., Diabetes Care., 33(11): 2477-8 (2010)). The number of people suffering from diabetes, obesity, hypertension, and heart disease is increasing every year. Today the major goal of diabetes management is control of blood glucose. As an alternative to sugar, which produces calories when it is metabolized in the body, artificial sweeteners are receiving much more attention. However, sugar cannot simply be replaced by intense sweeteners because of the factors of bulk, quality, intensity of sweetness, and physical characteristics. Artificial sweeteners get a bad reputation due to their unwanted/unexpected/nonpleasant taste and the issue of safety. Due to these features of artificial sweeteners, rare sugars are desirable for low calorie as well as bulk sweeteners. These sugars tend to have desirable sweetness but are not metabolized in the human body and therefore do not provide calorie intake. Therefore, there is high demand/need to have natural sugars with the desired quantities of sweetness, low caloric value, and least observed physiological effects. In addition to plant derived natural sweeteners, next generation natural sweet molecules are produced from microorganisms by using recycled oil and sugar sources. Arabitol, a sugar alcohol which is a stereoisomer to xylitol, produced using Debaryomyces hansenii, has the potential application as a sweetener for diabetic patients and reducer of dental caries (Koganti, S., and L.-K. Ju, Biochem. Engineer J., 79: 112-119 (2013)).
Another of the primary taste qualities is bitter, a sensation that arises when specific chemicals are detected by specialized receptors in the tongue. Bitter taste is thought to have evolved as a deterrent against ingesting toxic substances, which may explain why many drugs taste bitter. The T2R family of taste receptors functions as bitter taste receptors (Bachmanov and Beauchamp 2007; Bachmanov et al. 2014). Most T2Rs that have been studied have binding profiles that involve several different bitter-tasting ligands. Many active pharmaceutical ingredients and/or inactive ingredients in medicines and over the counter (OTC) preparations taste bitter and thus are aversive to children as well as many adults (Mennella, J. A., et al., Clin. Ther., 35(8): 1225-46 (2013)). With respect to OTC preparations, such as cough and cold syrups, the bitterness of the preparation leads to lack of patient compliance. Conventional taste masking methods, such as the use of sweeteners, amino acids, and flavoring agents, alone are often inadequate at masking the taste of highly bitter drugs. Another approach is to use bitter blockers, which instead of masking bitter taste by additional flavor eliminate it. It is, therefore, desirable to provide compounds that may be added to food products, consumer products, and pharmaceuticals comprising bitter tastants or having a bitter taste to eliminate, modulate or reduce the perception of the bitter tastants or bitter taste or to reduce the corresponding activation of the bitter receptors (e.g., in the oral cavity and/or the gastrointestinal tract). Similarly, it is desirable to provide food products, consumer products, and pharmaceutical compositions comprising such compounds.
We have found that sophorolipids have both sweet-tasting and bitter-blocking properties.